I have two solutions that I know of to fix your resource pack, solution two worked for me so.. If you're still wondering on how to get your resource pack to work I suggest reading this :))!! Solution 1: Just install optifine, rejoin the server with the resource pack on enabled, and it will download once you join. Solution 2: If you installed optifine, and it still doesn't work, you go to .minecraft > server-resource-packs > then delete everything in your server-resource-packs folders, and rejoin the server with the resource pack on enabled after. If none of these work, just ask on the discord in the #help channel. I also suggest trying out solution number one first, and then move on to solution two if solution one doesn't work.